EMPs aren't really a plausible weapon. Sure you can detonate a nuke, but by that time, you've already launched an ICBM, so you're screwed because of mutually assured destruction.
If you want disrupt an electrical grid, there's a lot of easier -- and less likely to have an obvious calling card -- than setting off a nuke.
And if you're thinking about some other type of EMP weapon, forget it. They're not practical. While a theoretical weapon, they're not a realistic one. It's fantasy.
Or you have your nuke already in place because you violated that treaty about nuclear weapons in space and can set it off without launching a rocket first.
If you want disrupt an electrical grid, there's a lot of easier -- and less likely to have an obvious calling card -- than setting off a nuke.
And if you're thinking about some other type of EMP weapon, forget it. They're not practical. While a theoretical weapon, they're not a realistic one. It's fantasy.
https://www.vice.com/en_us/article/kwxq4v/we-asked-a-militar...
https://nationalinterest.org/blog/buzz/world-wont-end-danger...